Cannot send `$upstream_addr` in a header?

[Michal Rus]

In a location block, I’m trying to do:

location / {
  proxy_pass http://falcon-backend-driving-fr/query;

  more_set_headers 'X-Upstream-Content-Type: $upstream_http_content_type';
  more_set_headers 'X-Upstream-Addr: $upstream_addr';
}

The first line with X-Upstream-Content-Type works, while X-Upstream-Addr is not added at all. I’m not sure, how to proceed…